<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var i = 5;   //整数
    var f = 3.14;  //浮点
    var b = true;  //布尔
    var c = 'a';  //字符串
    var str = "abc";   //字符串
    var d = new Date();  //日期
    var u;   //未定义类型
    var n = null; //空
    document.write("整数：" + typeof(i) + "<br/>");
    document.write("浮点 ：" + typeof(f) + "<br/>");
    document.write("布尔：" + typeof(b) + "<br/>");
    document.write("字符：" + typeof(c) + "<br/>");
    document.write("字符串：" + typeof(str) + "<br/>");
    document.write("日期：" + typeof(d) + "<br/>");
    document.write("未定义的类型：" + typeof(u) + "<br/>");
    document.write("null：" + typeof(n) + "<br/>");
</script>
</body>
</html>